Photohalogenation of hydrocarbons



United States Patent 3,428,539 PHOTOHALO-GENATION 0F HYDROCARBONS George R. Lester, Mount Prospect, Ill., assignor to Universal Oil Products Company, Des Plaines, Ill., a corporation of Delaware No Drawing. Filed Feb. 11, 1965, Ser. No. 431,994 US. Cl. 204-163 Claims Int. Cl. C07c 17/10 ABSTRACT OF THE DISCLOSURE Photohalogenation of a paraffinic hydrocarbon by treating said hydrocarbon with HBr, in the substantial absence of free halogen, at a temperature of from about ambient to about 150 C., a pressure of 1-50 atmospheres, in the presence of UV light having a wavelength of l800-2400 A.

This invention relates to a process for the photohalogenation of saturated hydrocarbons. More particularly, this invention is concerned with a process for the photobromination of paraiiinic hydrocarbons.

In recent years, the need for alkyl halides and particularly straight-chain alkyl halides of relatively long carbon atom length as intermediates for the preparation of many useful chemical compounds has increased. The alkyl halides are useful as intermediates in the formation of olefins which are formed upon dehydrohalogenation of the alkyl halides. These olefinic hydrocarbons are useful starting materials for the preparation of such varied compounds as rubber, plasticizers, detergents, etc. For example, the halogenation of n-butane will lead to the formation of halobutanes which, upon dehydrohalogenation, will form butadiene in the event that the halobutane contains 2 halogen substituents. The butadiene thus formed is an important starting material for the formation of synthetic rubber. In addition, relatively long straight-chain alkanes may be halogenated and thereafter dehydrohalogenated to form alpha-olefins which are useful as plasticizers in the formation of synthetic plastics and resins, said plasticizers imparting desirable physical characteristics to the finished product. Yet another chemical intermediate that may be prepared according to the process of this invention comprises alkylating agents which are useful in the preparation of detergents. Heretofore, detergents comprising long chain alkylaromatic sulfonates have been prepared and used as such. However, many of these long chain alkyl substituents were highly branched in configuration. The increasing use of detergents of this type has resulted in contamination or pollution of many streams, rivers, lakes, pools, etc., inasmuch as it has now been discovered that detergents of this type are non-biodegradable. In this respect the sight of streams, rivers, etc., containing amounts of foam has become increasingly prevalent. In addition, many communities have reported that where individual household septic tanks are involved, it has become likely that tap water is heavily laced with suds due to the contamination of said tanks. In addition, the water supply for cities or towns, which depend upon streams or rivers as a source of water supply is also contaminated. In order to combat this disadvantage, detergents which are prepared and used both now and in the future must, of necessity, be biodegradable in nature. These biodegradable detergents must contain long chain alkyl substituents which are "ice straight-chained in configuration or which may contain a minimum amount of branching, said branching preferably comprising no more than methyl radicals. This straightchain configuration of the alkyl side chain will permit the organisms which destroy the detergent to, in effect, eat their way up the chain, thereby destroying the molecules and allowing the detergents to be assimilated in the water Without concurrent production of undesired long-lasting foam or suds.

A particular source of relatively straight-chain alkyl radicals which may be utilized as a starting material for the preparation of biodegradable detergents comprises normal aliphatic paraffinic hydrocarbons which are separated from isomeric mixtures of normal and branched chain parafiins by any means well-known in the art. These long-chain aliphatic paraffinic hydrocarbons, preferably ranging from about 9 or 10 to about 16 carbon atoms in length will, after treatment thereof, be utilized as alkylating agents for benzene or toluene to prepare biodegradable detergents. Such pre-treatment may consist in the halogenation of the aliphatic parafiinic hydrocarbon whereby an alkyl halide of desired configuration is produced.

It is therefore an object of this invention to provide a process for the photohalogenation of saturated hydrocarbons.

A further object of this invention is to provide a process for the halogenation of saturated hydrocarbons, and particularly paraffinic hydrocarbons whereby the halogenating agent may be recovered for reuse.

In a broad aspect, one embodiment of this invention is found in a process for the photohalogenation of a saturated hydrocarbon which comprises treating said hydrocarbon with a hydrogen halide at halogenation conditions in the presence of ultra-violet light, and recovering the resultant halogenated hydrocarbon.

A further embodiment of this invention is found in a process for the photobromination of a paraffinic hydrocarbon which comprises treating said hydrocarbon with hydrogen bromide at a temperature in the range of from about ambient to about C. and at a pressure in the range of from about atmospheric to about 50 atmospheres in the presence of ultraviolet light having wave lengths in a range of from about 1800 to about 2400 A., and recovering the resultant brominated parafiinic hydrocarbon.

A specific embodiment of this invention is found in a process for the photobromination of n-dodecane which comprises treating said n-dodecane with hydrogen bromide at a temperature in the range of from about ambient to about 150 C. and at a pressure in the range of from about atmospheric to about 50 atmospheres in the presence of ultraviolet light having wave lengths in a range of from about 1800 to about 2400 A., and recovering the resultant brominated n-dodecane.

Other objects and embodiments will be found in the following further detailed description of the invention.

As hereinbefore set forth, the present invention is concerned with a process for the photohalogenation of saturated hydrocarbons and particularly straight-chain paraffinic hydrocarbons. Heretofore, in the halogenation of hydrocarbons and particularly paraffins, the process is usually carried out with either free halogen or substances which are capable of liberating free molecular halogen under reaction conditions. Examples of such halogenating agents include chlorine, bromine, phosphorus bromide, phosphorus chloride, etc. However, the use of such materials requires a cyclic process which includes an essential oxidation step to recreate the starting halogenation agent after the haloalkane has been dehydrohalogenated. In many instances, this required oxidation step constitutes a particularly undesirable step in the entire process due to the cost involved. For example, the oxidation of hydrogen bromide to form elemental bromine is relatively expensive due to the cost of the equipment which is involved in the oxidation or recycling steps. The expense is due mainly to the metals or type of metals which may be used in the equipment because of the corrosive nature of the compounds which are involved. The process of the present invention, as hereinafter set forth in greater detail, overcomes or eliminates this expense by eliminating the oxidation step required in the prior art and therefore will allow the photohalogenation of parafiinic hydrocarbons in a cyclic process to be accomplished in a relatively inexpensive manner as compared to the processes which are currently employed.

In the process of the present invention, a saturated hydrocarbon and particularly a parafiinic hydrocarbon which is straight-chain in configuration is subjected to photohalogenation by treatment with a halogenating agent in the presence of ultraviolet light. More particularly, the invention is concerned with the photobromination of paraf finic hydrocarbons utilizing hydrogen bromide as the brominating agent. The photobromination is carried out by subjecting the paraflin to the action of the hydrogen bromide in the presence of an ultraviolet light which has wave lengths in the range of from about 1800 to about 2400 angstrom units. Ordinary photobromination which is effected in the presence of elemental bromine will be carried out at wave lengths in a range below about 5000 angstrom units, this light causing elemental bromine to dissociate to atoms. When ultraviolet light, having a wave l ngth below 2500 angstrom units is used, hydrogen bromide will dissociate. However, there is only a weak absorption by HBr at about 2500 angstrom units, therefore, the ultraviolet light which is utilized should have wavelengths in the range of from about 1800 to about 2400 A., in order to obtain the maximum reaction rate of the dissociated hydrogen bromide with the paraffinic hydrocarbon. The ultraviolet light source may be obtained by any means known in the art, a particular source of energy being from a mercury or hydrogen arc, the energy being passed through a quartz crystal to dissociate the hydrogen bromide into hydrogen and bromide atoms. In addition, to having the light source be of such a variety so as to provide an ultraviolet light with wave-lengths within the range of [from about 1 800 to 2400 angstrom units, the photobromination is carried out at temperatures ranging from about ambient (25 C.) up to about 150 C. The process is also effected at pressures ranging from atmospheric up to about 50 atmospheres or more. In the present embodiment of the invention, the process is effected at elevated pressures ranging from about 10 to about 50 atmospheres in order that the photobromination be effected in the liquid phase. By utilizing the greater pressures and a liquid phase operation a higher conversion of parafiinic hydrocarbons to brominated hydrocarbons will be achieved due to the increase-d solubility of the hydrogen bromide.

By utilizing the hereinbefore stated operating conditions of ultraviolet wave length, temperature and pressure, a certain selectivity of halogenation and particularly bromination will beachieved, whereby a preponderance of monohalo parafiinic hydrocarbons form. When utilizing a pure paraflinic hydrocarbon as a feed-stock it will be found that about 95% of the bromine which is used will be incorporated in the parafiinic hydrocarbon as a monobromide. In the event that a polyhalo parafiin such as dibromide is required, the process may be effected in two stages in order to obtain a commercially attractive yield. For example, the paraflinic hydrocarbon may be passed through jected to photobromination according to the process of this invention preferably comprise those parafiins containing from about 2 to about 18 carbon atoms such as ethane, n-propane, n-butane, n-pentane, n-hexane, n-heptane, noctane, n-nonane, n-decane, n-undecane, n-dodecane, ntridecane, n-tetradecane, n-pentadecane, n-hexadecane, nheptadecane, n-octadecane, etc.

The process of the present invention may be effected in any manner and may comprise either a batch or continuous type operation. In the preferred embodiment of the invention, the process will comprise a continuous type operation in which the parafiinic hydrocarbon which is to undergo photohalogenation is continuously charged to a halogenation chamber. This chamber is maintained at the proper operating conditions of temperature and pressure within the ranges hereinbefore set forth in greater detail. In addition, the halogenating agent which preferably comprises hydrogen bromide although hydrogen chloride and hydrogen iodide, etc., may also be used is also continuously charged to the halogenation chamber at a predetermined rate. The halogenation chamber is provided with a source of ultraviolet light such as a mercury lamp which passes through a quartz lens so that the ultraviolet light enters the photohalogenation chamber at wave lengths ranging from about 1800 to about 2400 angstrom units. Upon completion of the desired residence time, the halogenated paraflinic hydrocarbons are continuously withdrawn from the chamber. The contact time during which the parafiinic hydrocarbon and the halogenating agent are in contact with each other will range from about 10 seconds up to about 10 minutes; the contact time being determined upon the particular temperature and pressure which is being utilized. The halogenated hydrocarbons are then passed to a fractionating zone, if so desired, whereby they are separated into monohalogenated hydrocarbons and polyhalogena-ted hydrocarbons. Following this, the monohalogenated hydrocarbons are passed to a dehydrohalogenation chamber wherein said paraffinic hydrocarbons undergo dehydrohalogenation by any means well-known in the art. The desired olefinic straight-chain hydrocarbons are recovered and the hydrogen halide which is formed by the dehydrohalogenation is recycled for use as the halogenating agent. As hereinbefore set forth, the relatively costly step of oxidizing the halogen atom so that it can be reused as the halogenating agent is eliminated with the concurrent use of less expensive equipment for the complete operation.

It is also contemplated within the scope of this invention that the process herein described may be eifected in a batch type operation. When this type of operation is used, a quantity of the parafiinic hydrocarbon is charged to a bromination chamber. The chamber is sealed and the halogenating agent comprising a hydrogen halide such as hydrogen bromide, is charged thereto. The apparatus is then adjusted to the desired temperature and pressure and the ultraviolet light from an external source is then turned on. Upon completion of the desired residence time, the chamber is allowed to cool to room temperature, the excess pressure is vented and the halogenated hydrocarbon is recovered therefrom. This hydrocarbon is then placed in a separate dehydrohalogenation apparatus where it undergoes dehydrohalogenation to form an olefin and hydrogen halide. The latter is recovered by any means well-known in the art and utilized as a portion of the feed stock for the halogenation step, the resultant olefin being recovered.

The following examples are given to illustrate the process of the present invention which, however, are not intended to limit the generally broad scope of the present invention in strict accordance therewith.

Example I To a photobromination apparatus which is provided with a quartz Window and a mercury lamp, is charged butane. The apparatus is maintained at a temperature of about 50 C. Hydrogen bromide is also charged thereto in such an amount so that the pressure is maintained at about 25 atmospheres. The mercury lamp is activated and an ultraviolet light having wave lengths of from about 1800 to about 2400 A. enters the chamber. After a contact time of about 5 minutes, the apparatus and contents thereof are allowed to cool to room temperature and the excess pressure is vented. Following this, bromobutane is recovered and placed in a dehydrohalogenation apparatus. In this apparatus, the n-bromobutane is dehydrohalogenated at a temperature of about 350 C. and at a pressure of about 1 atmosphere. The desired product comprising a mixture of l-butene and 2-butene is recovered, while the hydrogen bromide is collected and utilized as a portion of the feed stock for the initial brominatin-g step.

Example II In this example, a photobromination apparatus is maintained at a temperature of about 50 C. and under applied pressure of about 25 atmospheres. N-dodecane is continuously charged thereto through one line while hydrogen bromide is also continuously charged thereto through a separate line. The mixture is subjected to continual stirring while an ultraviolet light from a hydrogen arc lamp passes through a quartz window, said light having Wave lengths of from about 1800 to about 2400 A., into said apparatus. The reactor efiluent comprising a mixture of n-dodecane, monoand dibromododecanes is continuously withdrawn and passed through a fractionating column. In the fractionation column, the n-dodecane is separated and recycled to form a portion of the feed stock, while the monobromododecane and polybromododecanes are also separated. The monobromododecane is continuously passed to a dehydrohalogenation unit, wherein said compound undergoes dehydrobromination. The desired n-dodecane is passed to storage while the hydrogen bromide which is formed upon dehydrobromination is recycled to form a portion of the halogenating agent which is utilized in the first step of the reaction.

Example III In this example, n-undecane is continuously charged to a photobromination unit similar to that set forth in Example II above. Upon completion of the desired contact time, the brominated undecane, both monoand polybrominated in nature, are continuously withdrawn and passed to a fractionation zone wherein the unreacted undecane is separated from the brominated undecane. In addition, the mon-obromoundecane and polybromoundecanes are also separated and passed in their respective streams to dehydrobromination units. In these units, the respective brominated undecanes are dehydrobrominated and passed to storage as n-undecene and n-undecadiene while the hydrogen bromide which is recovered from the dehydrobromination is recycled to the photobromination unit.

Example IV In a manner similar to that set forth in the above examples, n-decane and n-hexadecane are subjected to photobromination in the presence of an ultraviolet light having a wave length of between 1800 and 2400 A. Upon completion of the photobromination, the brominated hydrocarbons are subjected to dehydrobromination reactions and the monoand polyolefin compounds recovered therefrom. In addition, the hydrogen bromide which is recovered from the dehydrobromination step is recycled to form a portion of the halogenation agent required in the first step of the process.

I claim as my invention:

1. A process for the photohalogenation of a saturated hydrocarbon which comprises treating said hydrocarbon with a hydrogen halide, in the substantial absence of free halogen, at halogenation conditions in the presence of ultra-violet light, and recovering the resultant halogenated hydrocarbon.

2. A process for the photohalogenation of a saturated hydrocarbon which comprises treating said hydrocarbon with a hydrogen halide, in the substantial absence of free halogen, at halogenation conditions in the presence of ultra-violet light having wave lengths in a range of from about 1800 to about 2400 A., and recovering the resultant halogenated hydrocarbon.

3. A process for the photohalogenation of a saturated hydrocarbon which comprises treating said hydrocarbon with a hydrogen halide, in the substantial absence of free halogen, at a temperature in the range of from about ambient to about C. in the presence of ultra-violet light having wave lengths in a range of from about 1800 to about 2400 A., and recovering the resultant halogenated hydrocarbon.

4. A process for the photohalogenation of a parafiinic hydrocarbon which comprises treating said hydrocarbon with a hydrogen halide, in the substantial absence of free halogen, at a temperature in the range of from about ambient to about 150 C. and at a pressure in the range of from about atmospheric to about 50 atmospheres in the presence of ultra-violet light having wave lengths in a range of from about 1800 to about 2400 A., and recovering the resultant halogenated paratfinic hydrocarbon.

5. A process for the photobromination of a paraflinic hydrocarbon which comprises treating said hydrocarbon with hydrogen bromide, in the substantial absence of free halogen, at a temperature in the range of from about ambient to about 150 C. and at a pressure in the range of from about atmospheric to about 50 atmospheres in the presence of ultra-violet light having wave lengths in a range of from about 1800 to about 2400 A., and recovering the resultant brominated paraffinic hydrocarbon.

6. The process for the photobromination of butane which comprises treating said butane with hydrogen bromide, in the substantial absence of free halogen, at a temperature in the range of from about ambient to about 150 C. and at a pressure in the range of from about atmospheric to about 50 atmospheres .in the presence of ultra-violet light having wave lengths in a range of from about 1800 to about 2400 A., and recovering the resultant brominated butane.

7. A process for the photobromination of n-decane which comprises treating said n-decane with hydrogen bromide, in the substantial absence of free halogen, at a temperature in the range of from about ambient to about 150 C. and at a pressure in the range of from about atmospheric to about 50 atmospheres in the presence of ultra-violet light having wave lengths in a range of from about 1800 to about 2400 A., and recovering the resultant brominated n-decane.

8. A process for the photobromination of n-undecane which comprises treating said n-undecane with hydrogen bromide, in the substantial absence of free halogen, at a temperature in the range of from about ambient to about 150 C. and at a pressure in the range of from about atmospheric to about 50 atmospheres in the presence of ultra-violet light having wave lengths in a range of from about 1800 to about 2400 A., and recovering the resultant brominated n-undecane.

9. A process for the photobromination of n-dodecane 7 which comprises treating said ndodecane with hydrogen bromide, in the substantial absence of free halogen, at a temperature in the range of from about ambient to about 150 C. and at a pressure in the range of from about atmospheric to about 50 atmospheres in the presence of 5 ultra-violet light having wave lengths in a range of from about 1800 to about 2400 A., and recovering the resultant brominated n-dodecane.

10. A process for the photobromination of n-hexadecane which comprises treating said n-hexadecane with hydrogen bromide, in the substantial absence of free halogen, at a temperature in the range of from about 8 ambient to about 150 C. and at a pressure in the range of from about atmospheric to about 50 atmospheres in the presence of ultra-violet light having wave lengths in a range of from about 1800 to about 2400 A., and recovering the resultant brominated n-hexadecane.

References Cited UNITED STATES PATENTS 2,566,052 8/1951 Beanblossom 204-163 HOWARD S. WILLIAMS, Primary Examiner. 

